Abstract: A combustion engine comprising; a pair of opposed cylinder elements (2, 3) having a common axis, each cylinder element being provided with a piston (28) reciprocable between first and second locations in the cylinder element the first and second locations respectively representing compression and expansion elements of the piston stroke, each piston having a forward side and a rear side; a combustion chamber (38) for each cylinder element comprising the forward side of the piston (28) and the walls (2) of the cylinder element; combustible gas compression means (37b, 37c) for each combustion chamber; supply passage means (41) arranged to deliver combustible gas to each combustible gas compression means; an induction chamber (37a) for each piston arranged to receive compressed combustible gas from the combustible gas compression means; transfer passage means (39) for directing compressed gas from each induction chamber to the respective combustion chamber, and cam means (13) rotatable about the common axis the c